I was trying to book airplane tickets for my whole family, two adults, two children aged 8 and 3 on the website of the carrier. I can go though the entire booking process but when I click 'pay' I get the error message 'no infant tickets available for this flight'. I called the customer service and they claimed it should work.
My guess is that there is some bug in the booking software that treats children as infants (defined as 0 to 2 years old). The number of infant tickets can indeed be limited but a 3-year-old gets their own regular seat like an adult so I don't think any restrictions apply here.
The price difference between child and adult is neglible (10 euros because one small item out of a whole list of fees disappears) so I thought I could just try to book 4 adult tickets. Now my question is whether I could run into any problems if I have an adult ticket for someone born in 2019?